Group interviews to screen from a large pool of candidates in a shorter time. Apart from reducing lead time, group interviews also allow recruiters and managers to assess candidates in real-life atmosphere, engaging in inter-personal communication.

It's not the same for candidates, though. Many candidates get intimidated and go into their shell during the group interview. Others try a bit too much to grab the attention of the moderator. However, mastering a GD is, in fact, simple. All you have to do is listen, wait for your turn and unleash your awesomeness. And here are a few things you better avoid...
Turning up Late
This one's a no-brainer. Simply don't turn up late. You are wasting everyone's time. If it's a bigger group, you will be quite pleasantly surprized to find out the discussion has already started. And you are no longer invited.
No Credible Introduction
In most cases, the moderator will ask the candidate to introduce themselves. So prepare a well-framed introduction which highlights who you are, what your strengths are, and where your interests lie. A sound introduction might help you to ease off and start the overall discussion, catching the eye of the moderator.
Asking your Moderator for Help
You might find it a bit start to dive in right away into the discussion. But, do not rush and solicit help from the moderator either. Just bide your time and listen what others have to say. You will be surprized to find out that you have a lot to add to the conversation.
Not Listening to Others
While you are at the GD, pay your full attention to others. Do not space out, or have one-to-one conversations. It's plain disrespectful. Listening is as great a communication skill as speaking out loud. Furthermore, it will help you keep your arguments relevant and poised.
Being Close-minded
Any discussion will lead to diverse opinions from the participants. So be accomodative of others' opinions. Being too up-tight and confrontational will just prove how rigid and inflexible you are. Not exactly what employers are looking for.
Taking it as a Debate
It's called a group discussion, not a grand debate. Your aim should not be to impose your views on the whole group, and prove that you are right. In fact, avoid confrontation altogether. Instead, listen to others. If you differ from their opinion, frame your response politely, while not casting the original speaker in a poor light.
Repeating what's being said
Yeah, it's the oldest trick in the book. It's call parroting and every HR manager knows about it. If you don't have anything to add to the conversation, wait till something meaningful pops up. The key is to be unique and original. You don't have to agree, nor argue with everyone present.
Becoming the Self-Proclaimed Leader
It's excruciating. You cannot impose yourself as the leader of the group. You just get besteowed leadership. So, instead of trying to play smart, just go with the flow. Contribute to the conversation creatively and analytically. Be friendly. In most cases, taking these two simple steps ensures that you emerge as the leader.
Acting like the Moderator
Do not try to shepherd the group. The group might digress or come back to the same point. It's not upto you to warn them or proclaim it out loud. It just breaks the group dynamics. You can always think of an alternate view and divert the conversation in that direction.
Talking too much
If you keep blabbering, no one's going to listen to you. You might know a lot (or think you do). But then, you are not here on an educational mission. Rater, try to draw the conversation forward by engaging other participants, and dropping in timely words of wisdom!